But we’re still losing — failing to inspire and fully prepare — roughly half our children. Most are bright and curious, can be taught. Just check how many, even from the poorest neighborhoods, are “digital natives.” And all are needed in the new global economy. Which leads to:

Surprise No. 2: The school system as we know it — 20 to 30 children in a classroom, sitting mostly passively through instruction, moving grade-to-grade with preset courses in rigid sequence — is toast.

Surprise No. 3: A fascinating “disruptive technology” has started to displace big chunks of schooling. It’s called student-centric learning — individualized instruction, or better put, students progressing at their own pace, guided by computer programs tailored to their learning levels and personal learning strengths. A process in which teachers instruct less, coach more.

Prediction: In 10 years, computer-based, student-centric learning will account for 50 percent of the “seat miles” in U.S. schools. By 2024, roughly 80 percent of courses will be taught this way.

So who says all this? The answer is Clayton Christensen, Harvard Business School’s famed expert on how “disruptive technologies” challenge and displace long-dominant industries. Together with my colleague Curtis Johnson and Michael Horn of the Innosight Institute, Christensen is a co-author of a new book, “Disrupting Class,” just published by McGraw-Hill.

When businesses fail, according to Christensen’s 20 years of research, it’s usually because they’re highly proficient at — but have great difficulty abandoning — the processes they’ve excelled in. So rivals develop radically new products, often inferior at first, but reaching previously unserved customers and improving over time, disrupting and eventually taking over the field.

Example: The first transistor radios such as upstart Sony’s in the 1950s. The first were low quality but they were portable — so that kids could listen to rock music away from their parents. Before long, the big old tube-based radios (and many of their manufacturers) were history.

A similar disruption is now hitting America’s public schools with their century-old standardized grade levels and assumption that courses can be put in rigid sequence, taught to all kids of a similar age at the same time and speed. Like the industrialized factory on which they were modeled, the schools and their row-upon-row classrooms are rapidly being undermined by flexible new models designed to accommodate kids’ learning differences.

For evidence, check the number of home-schooled children — up from 850,000 in 1999 to more than 2 million today. Add to that the rapid rise of charter schools with their experimental, more flexible formats. And computer-based courses created by private firms. The computer-learning programs have skyrocketed from 45,000 in 2000 to roughly 1 million today, and they’re fast improving with enhanced video, audio and interactive elements, including formats to reach different types of learners. More than 25 states now have supplementary virtual schools.

If there were ever a “disruptive” technology, this is it! And it works precisely because our brains seem coded to learn in so many different ways — for some of us visually, others by taking notes, and with special intelligences ranging from linguistic to spatial to logical-mathematical.

Student-centric instruction allows adjustments to the optimal learning capacities of school pupils. Ironically, it’s a little bit like the one-room classrooms of the 1800s, in which teaching was customized by necessity as teachers spent most of their day going from student to student at different grade levels, providing personally tailored instruction and assignments.

But in 1900, only 50 percent of 5- to 19-year-olds were enrolled in school. The new demand then was to educate everyone, at least prepare everyone for vocations in an industrializing economy. Almost 60 years later came the Sputnik scare, obliging more focus on science and math. And we keep asking schools for more.

And now, with No Child Left Behind, we’ve moved the goal posts again, decided for a 21st-century economy it’s not enough for public schools to raise average scores, rather it’s to assure every child improves his or her test scores to qualify for a high skill- and knowledge-based employment.

The genius of “Disrupting Class” is the spotlight the book throws on how we can tap children’s early enthusiasm for school by letting them learn in best-choice, individualized ways, the teacher’s role transformed from “sage on the stage” to “guide on the side.”

Will teacher unions resist? That’s the great fear experts raised to the book’s authors. But with looming teacher shortages as the baby-boom generation retires, teachers may only have time for math and reading basics. The new wave of computer-based courses may, indeed, be arriving just in the nick of time.